The invention relates to a printing machine having at least one impression cylinder.
An impression cylinder is used for example in a flexographic printing press for pressing the print substrate against a printing cylinder. In this case, the print substrate is conventionally guided around the impression cylinder and is advanced by this cylinder. In order for the printing ink to be precisely transferred from the printing cylinder onto the print medium at the location of contact between the impression cylinder and the printing cylinder, it is necessary to precisely adjust an optimal distance between the cylinders, in order to achieve a printed image with a uniform high quality which meets the high quality standards that are commonly required today.
The diameter of the impression cylinder may for example be in a range from 2 m to 3.5 m. Given a linear thermal expansion coefficient of about 11×10−6 K−1 for steel, a fluctuation of the temperature of the impression cylinder by 5° C. results in a change in the external radius by an amount of approximately 55 μm to 95 μm. For this reason, a temperature stabilisation is applied in conventional printing machines in order to avoid inadmissible fluctuations in the radius of the impression cylinder. Thus, steel impression cylinders are known which have a two-fold external steel wall the interstice of which serves as a channel for tempering water.
When, for example, the environmental temperature in a print shop fluctuates between 15° C. and 35° C., a tempering system of the liquid coolant type permits to limit the temperature fluctuation of the impression cylinder to ±0.5° C. or ±1° C., whereby the necessary dimensional stability of the radius of the impression cylinder is assured.